Contamination in protein purification

A standard procedure in pufying tubulin is to extract the tissue on ice, then add GTP and warm the tissue extract to 37C. The warmed extract is then centrifuged at a speed insufficient to pellet average sized proteins, but sufficient to pellet large protein complexes. After centrifugation, the supernant is discarded, and the solution is agian warmed for a few minutes. Then centrifugation at the same speed described above is again performed. This process is repeated several times.

How would this processs result in purification of tubulin?

What contaminating proteins would likely co-purify with the tubulin?

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The extraction procedure results in dissociation of the cells. Usually this involves mechanical disruption, salt buffer, and chaotropic or non-chaotropic detergents. Large proteins like tubulin are relatively insoluable in most buffers. Therefore, through centrifugation they can be pelleted while other proteins enter solution and may be washed away and discarded. This will usually required repeated steps to ensure that smaller soluable proteins that bind to tubilin can be washed ...

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